I just did it a few weeks ago. If you normally deal with the UK CAA, then if you call Flight crew Licensing they will tell you specifically what you need to do.
What I did was as follows:
1. A 3 hour Skills test.
2. With the skills test paperwork, 500 hours+ on type in my logbook, the foreign License with type rating and current OPC, I went to CAA house at Gatwick, arrived at 7am and they had it on my EASA License by 9.30am